In the field of petroleum drilling and exploitation, the directional drilling technology is significantly important to improve recovery ratio of crude oil and stabilize oil field output. Especially for complex hydrocarbon reservoir, the drilling-encounter ratio and well trajectory control has always been the main factors to restrict cost reduction of drilling and exploitation while the accurate information and data on the formation where the drill bit is located plays a decisive role to realize the favorable drilling-encounter effect. Thus, the technology on geological steering of drilling becomes the indispensable key technology for the directional well development. The technology on geological steering of drilling for directional well confirms and controls the well trajectory based on the actual geological features, and then controls accurately downhole motor to hit the target formation. The key technology for allowing the drill to encounter the optimal target formation, also named effective reservoir, is to control well trajectory, ensure the drill bit to penetrate in the effective reservoir and avoid the encountering on interlayer to the greatest extend.
The measurement while drilling instrument with conventional method for measurement while drilling is set upon the motor, and the measurement position is normally located beyond 10 meters from the lower surface of motor system. During drilling, because of the long distance between drill bit and measurement instrument, the data and information for the formation where the drill bit is located cannot be accurately measured in real time, frequently causing that the drill bit penetrates out of hydrocarbon reservoir, particularly the thin hydrocarbon reservoir.
The application of conventional near-bit measurement while drilling is able to conquer the defect that the data and information for the formation where the drill bit is located fail to be measured accurately in real time. The short sub of near-bit measurement while drilling system is set at the lower position of motor system and is connected with drill bit directly so that the measurement location is near the drill bit. However, due to the adding of short sub for the measurement while drilling between drill bit and motor system, the distance between drill bit and bent point of motor is increased, which will cause the lowering of controllability on drill bit and the increasing of friction and torque for the downhole motor at the bottom hole as well as the raising of vibration of drill bit during operation. Because the short sub for measurement while drilling is added for the conventional near-bit measurement while drilling, the structure of the bottom hole drilling tool combination has been changed and then causes the change of mechanical characteristics, which lead to the decreasing of deflecting capability of downhole motor. Thus the controllability on well trajectory is insufficient and the frequent hysteresis on control of well trajectory causes long time for hole straightening. The impact caused from vibration of drill bit in the process of operation aggravates the damage of bottom hole tools. Moreover, when the data and information from conventional near-bit measurement while drilling method are transmitted to receiving device through wireless mode, the wireless transmitting signals must penetrate the obstacle of downhole motor system, thus leads to long transmitting distance and signal transmission without stability and reliability.
The objective of the invention is to: focusing on the existing problems mentioned above of fields on drilling and exploration, provide a near-bit measurement while drilling system which is able to measure the data and information of formation where the drill bit is near and which can acquire the data and information of the formation where the drill bit is located and well trajectory parameters more accurately in real time for the realization of improving drilling-encounter ratio of drill bit, maintaining high guiding and control capability on drilling tools, enhancing well trajectory controllability, improving recovery ratio and reducing drilling cost.
The Objective of the Invention Shall be Realized Through the Following Technical Solution:
A near-bit measurement while drilling system contains motor system, measurement transmission system, wireless receiving system and non-magnetic short sub. The motor system is composed of the external housing and the internal rotation part, and the non-magnetic short sub is set upon the motor system. Meanwhile, the non-magnetic short sub and the motor system are connected directly or through drilling tools or via short sub. A hole is set inside the internal rotation part of the motor system. The measurement transmission system contains a measurement device of data acquisition and data measurement, a transmitting device of the wireless receiving system to which the data of the measurement device is transmitted, a transmission device of transmitting device to which the data of measurement device is transmitted, and a power supply device for supplying electric energy to the measurement device and the transmitting device. The measurement device and the transmission device of the measurement transmission system are set inside the hole of the internal rotation part of the motor system. The measurement device is set within ⅓ lower position of the motor system and within 2 meters from the bottom surface of the motor system. The transmitting device of the measurement transmission system is set at the upper position of the internal rotation part of the motor system and extends into the non-magnetic cavity. The measurement transmission system is relatively fixed with the rotation part of the motor system and is able to rotate along with the external housing of motor system together with the internal rotation part of the motor system. The wireless receiving device of the wireless receiving system is set inside and relatively fixed with the non-magnetic short sub. When the motor system is in operation, the measurement transmission system makes relative rotation upon the wireless receiving system, and the wireless receiving device and the transmitting device will transmit signals through wireless transmission.
Preferably, the measurement device is set within 1.5 meters from the bottom surface of the motor system. Further preferably, the measurement device is set within 1 meter from the bottom surface of the motor system.
Preferably, the motor system belongs to downhole motor system, a excellent motor tool in the aspect of oriented drilling, which is able to provide large torque and high rotation speed and which is capable of admirable performance on oriented drilling. Meanwhile, with the compact structure, the downhole motor system is applicable in drilling at directional well and clusters well. The combination of downhole motor system and the measurement while drilling system is capable of making deflection, orientation and deviation correction, which will improve project quality and reduce drilling cost.
Further preferably, the rotation part of the downhole motor system includes at least a drive shaft, a universal shaft and a rotor. The measurement device is set inside the drive shaft of the downhole motor system, which is relatively fixed with the drive shaft and is able to rotate together with the drive shaft. Through the direct connection of the drive shaft from the downhole motor system and the drill bit, the measurement device is very close to the drill bit so that the data and information where the drill bit is located can be accurately measured in real time. Because the measurement device is set in the inner part of the drive shaft, there is no increasing of distance between the drill bit and the motor bend point so as to enhance the guiding controllability of drill bit, reduce the friction and torque in bottom hole compared with those where the short sub is added between the drill bit and the motor, and decrease the vibration of drill bit during operation. Furthermore, the drilling tools will keep high capability of deflection and hole straightening, ensure the quality of well trajectory, reduce drilling cost, raise recovery ratio, decrease transmission resistance, improve drilling efficiency, bring down the vibration impact of drill bit at bottom hole and thus reduce the damage caused by the vibration impact on the downhole tool such as the drill bit.
Further preferably, the transmitting device is set at the upper position of the rotor. The transmitting device is relatively fixed with the rotor and is able to rotate together with the rotor. The transmitting device is set at the upper position of the rotor so that the transmitting device is close to the receiving device of the wireless receiving system. And no obstacle exists between the transmitting device and the receiving device as for signal transmission. Meanwhile, the entire measurement while drilling system is able to rotate together with drill bit in order to effectively protect the measurement transmission system.
Preferably, the power supply device of the measurement transmission system is set inside the hole of the internal rotation part of the motor system, which is located between the measurement device and the transmitting device and more close to the transmitting device. The power supply device provides reliable power supply for the measurement transmission system to ensure the continuous and stable operation of the measurement transmission system.
Preferably, the measurement device contains an azimuth gamma sensor and a well deviation sensor. The azimuth gamma sensor is used for acquisition of azimuth gamma data and the well deviation sensor is used for measurement of well deviation data. In the process of directional drilling, the data of azimuth gamma and well deviation of the formation where the drill bit is located is the primary and most important basic data, which directly determines the quality of well trajectory and drilling-encounter ratio, and which affects the recovery ratio and drilling cost.
Preferably, the safety anti-drop assembly is set between the motor system and the non-magnetic sub. The safety anti-drop assembly contains safety an anti-drop sub and a safety anti-drop cap. A through-hole in the center of the safety anti-drop cap with axial penetration is set at and fixed with the upper position of the internal rotation part of the motor system. The transmitting device of the measurement transmission system penetrates the through-hole in the center of the safety anti-drop cap and extends into the non-magnetic safety anti-drop cavity. The lower position of the safety anti-drop sub is connected with the external housing of the motor system, and the upper position is connected with the non-magnetic short sub. Meanwhile, the limit shoulder is set at the inner wall of the lower position of the safety anti-drop sub. The flange is set at the outer wall of the upper position of the safety anti-drop cap and is used to catch the inner part of the motor system at the limit shoulder in case of the fracture of lower part of housing. The safety anti-drop assembly is able to prevent the motor system from dropping into bottom hole in case of housing fraction so as to reduce the salvage cost and drilling risk and thus to improve the safety and reliability of the patent. Preferably, the non-magnetic short sub is a non-magnetic collar. When the non-magnetic short sub is directly connected with the motor system, the transmitting device of the measurement transmission system will extend into the cavity of the non-magnetic collar. The signals are transmitted wirelessly between the transmitting device and the receiving device in the patent, and the magnetically short connection will interfere and influence the stable and reliable transmission of wireless signals. Meanwhile, as one part of the drilling pipe, the non-magnetic collar also performs the stabilization effect without impacting on the transmission of wireless signals.
The main scheme and various further preferable selection schemes in the invention are able to form multiple schemes through independent assortment, which shall be applied and required to protect in the invention. Meanwhile, the selection schemes themselves without selection conflict from each other are also able to be combined freely. The technicians in this field are able to clearly identify multiple combinations after understanding the invention scheme based on the existing technology and common general knowledge. Those technical solutions shall all be protected in the invention, and will not be listed in exhaustion.
The beneficial effect in the invention: For the near-bit measurement while drilling system in the invention, the measurement device is set near the drill bit inside the motor system so as to measure the real-time data and information as well as the well trajectory parameters for the formation where the drill bit is located more accurately during drilling on the one hand, and is capable of transmitting the measured data and information wirelessly in real time stably and reliably to the receiving device of the wireless receiving system. The measurement while drilling system is set inside the motor system and will keep the drilling tool with capability of high deflection and hole straightening.
Compared with the conventional method for measurement while drilling, the measurement position in the invention is within 2 meters (even short such as within 1.5 meters and within 1 meter) from the lower surface of the motor system and is close to the drill bit. Hence, the data and information for the formation where the drill bit is located is able to be measured more accurately in real time in the process of drilling so as to effectively avoid the drill bit penetrating the hydrocarbon reservoirs, especially the thin ones, which improves the drilling-encounter ratio of the oil layer and performs the non-hysteretic description of well trajectory significantly.
Compared with conventional method for near-bit measurement while drilling, the measurement device in the invention is set between the drill bit and the bend point of deflection without any influence on the distance between the drill bit and the bend point (There is no need to add any short sub or tool between the drill bit and the motor, thus the distance from the drill bit to the motor or bend point does not increase) so as to enhance the guiding controllability of drill bit, reduce the friction and torque in bottom hole compared with those where the short sub is added between drill bit and motor, and decrease the vibration of drill bit during operation. Furthermore, the drilling tools will keep high capability of deflection and hole straightening, ensure the quality of well trajectory, reduce drilling cost, raise recovery ratio, decrease transmission resistance, improve drilling efficiency, bring down the vibration impact of drill bit at bottom hole and thus reduce the damage caused by the vibration impact on the downhole tool such as the drill bit. On the other hand, compared that the data and information is transmitted to the receiving device of the receiving system wirelessly as for the conventional method of near-bit measurement while drilling, the wireless signals in the invention will be directly transmitted to the transmitting device near the receiving device of the wireless receiving system through the transmission device of the measurement transmission system (wire transmission) and then transmitted to the receiving device wirelessly without penetrating through the downhole motor system, which largely shortens the transmission channel for the wireless data transmission with no obstacles and enhances the stability and reliability of the signal transmission.
The near-bit measurement while drilling system in the invention is characteristic of compact structure and the measurement transmission system is set inside the motor system, which solves the problem on the acquisition of the data and information for the formation where the drill bit is located and well trajectory parameters more accurately in real time for the realization of improving drilling-encounter ratio of drill bit, maintaining high guiding and control capability on drilling tools, enhancing well trajectory controllability, improving recovery ratio and reducing drilling cost. Meanwhile, the wireless communication transmission in short distance without obstacles can be realized between the transmitting device of the measurement transmission system and the receiving device of the receiving system so as to fulfill the short-distance test and transmission, thus improving the stability and reliability of data transmission. The measurement device is very close to the drill bit in the invention. The more the measurement device is close to the drill bit, the more accurately the real-time data and information as well as parameters of well trajectory for the formation where the drill bit is located are measured in the process of drilling, and the higher drilling-encounter ratio and recovery ratio of the drill bit is.